Help with electronics upgrade

[RickWyatt]

Hi everyone.

I am happy to say that I have paid off my machine paid off my machine in the 3 short months that I have had it! However, I desperately need to improve my quality of cut if I can with this machine:

Older PRT with Porter Cable Router (just re-built)
Vexta Motor A6497-9412KTG 2 Phase .5 Degree Step
2001 control box version 3.2 (with jumper on 1/4)
Vectric VCarve Pro 5.5 w/Shopbot arcs inch Post Processor


I have called Shopbot and was very happy with the results I received with helping to tweak my unit values:

X-733.386
Y-733.386
Z-916.7325
Circle Res: .005


Here is my issue: I am familiar with proper tools feeds/speeds/chiploads. My table is square, level and plumb. However, I am getting quite a bit of chatter on the edge of my material. Even in something as soft as 15 lb Precision Board.

I realize that it won't be perfect, but it should be better than what I'm getting.

I feel a lot of "mechanical vibration" when my machine moves in x and y axis. If I Put my hand on the Y carriage, I can fell it "Mechanically shake" during all types of movements.

I would like to upgrade the control box to the electronics I have posted here with pics. I was given these parts when I purchased the machine. But, I don't know much about this end of it. I was hoping someone could point me in the right direction with a schematic or be able to see what I'm missing. I have no idea how to wire this up.:confused:

I have:

4 Gecko G201 uSTEP DRIVES
C-11 Multifunction CNC Breakout Board from CNC4PC
Torridal Transformer
Power Supply (looks to be from a computer)
Mach 3 software on the computer that came with machine


Thanks for all of the information everyone has provided on this forum. It has been a huge help. If someone can help me with this upgrade, I was thinking of making a video of the steps and post a link to it here for others in the future.

Thanks,

Rick Wyatt

[Dusty Knobel]

If you are not going to follow the Shopbot upgrade path (4g - highly recommended), - go to www.mechmate.com. They have discussions on creating your own controller and software needed to use it, and on how to improve your gantry, which is what I did.

Dusty
Olympia, WA

[cnc_works]

When I upgraded my ShopBOT PRT to Mach 3 and gecko it improved my edge cut a great deal. Still nothing to brag about but it is seldom a real problem whereas before the conversion it was unacceptable. I also appreciated a significant increase in rapids and cut speed.

The only thing I regret is that when I made my conversion the 4G was still not available so I stepped out of the ShopBOT family and now have a hybrid. It has not been a major problem but there have been times that troubleshooting was a little more difficult. Thankfully, there are other forum members with similar setups who have been generous with technical help.

Bottom line, dollar for dollar I would buy the ShopBOT upgrade. However, there are many resources to put one together for yourself and save dollars.

[ken_rychlik]

They offer the 4g upgrade for about 1500 dollars, but they may fix you up without geckos for less money. It would be worth a phone call to tell them what you have and see what they could offer.

Also your old board has some value. There are a few people that have a need for a replacement board.

[RickWyatt]

Thanks for everyone's quick replies... The only reason I haven't gone for the Shopbot 4g upgrade is the fact that it looks like I have most if not all of the parts required. These all came with the cost of my machine.

The next major purchase will be towards a new machine. But, for now, upgrades will have to do.

[ken_rychlik]

When you upgrade, a machine with the 4g upgrade will be worth more and easier to sell, than a retro mach machine.

If you sell all of your parts and sell your old board, it would not cost that much for a 4g upgrade.

If you decide to create your own, the mechmate site will be the place to dig up all the info you need. If you search deep enough, you can find wiring diagrams also. Most of them will be with a pmdx 122 board though and not with the board you have.

Good luck whatever you decide.

[richards]

Rick,

The other posters have given good advice. Those parts that you have will give you significant improvement over the drivers that you are now using, BUT, they are meant to be used with G-Code, not SB3 software.

There are a lot of photos and comments on the MechMate forum that describe exactly how to connect everything together, but remember, if you use those parts, you'll have to change to G-code.

With that said, here's a very brief overview of what you'll need to do:

1. Build a power supply. Hopefully the toroidal transformer is a 50VAC to 55VAC unit so that it can provide 70 to 80VDC. (I'm assuming that you have motors with four wires where the A-coil has black and green wires and the B-Coil has red and blue wires.) A 250VA or 300VA transformer is adequately large. Verify that the bridge rectifier can handle 200V at 10A. (I always buy the 400V / 35A units. They only cost a little more than the 50V units.) Finally, you'll need one or more filter capacitors. Those motors don't require much current so 6,000uF would be the minimum that I would use. Because of the high voltage, get the 200V units.

The transformer changes the line voltage to about 50VAC. The bridge rectifier turns a 60-cycle full wave to a 120-cycle half wave. The capacitor(s) filter out the AC and creates a DC voltage with very little AC ripple.

2. Connect the G201 stepper drivers to the motors and to the Power Supply. The G201 stepper drivers require that you add a 470uF capacitor to the + and - power supply connections.
- Connect the power supply's - DC voltage to Terminal 1.
- Connect the power supply's + DC voltage to Terminal 2.
- Connect the motor's Black wire to Terminal 3
- Connect the motor's Green wire to Terminal 4
- Connect the motor's Red wire to Terminal 5
- Connect the motor's Blue wire to Terminal 6
- Connect one end of a 10k 1/4w resistor to Terminal 11
- Connect the other end of that resistor to Terminal 12

(You can use a resistor with values from about 7.8k to about 13k. The higher the value, the more current that the motor is allowed to pull and the hotter the motor/driver will run. Because the power supply is well below the optimum voltage for that motor, you can increase the current without overheating the motor. 7.8 K = 1A and 12.8K = 1.5A)

I recommend mounting the stepper drivers onto a heat sink. A piece of 1/4-inch thick aluminum should work fine as long as air can circulate inside the controller.

Also, select auto current reduction on the option jumper block (inside the stepper driver).

Tune the stepper drivers as described in the manual (available for download from www.geckodrive.com).

(While you're downloading the manual, also download the 'Stepper Motor Basics' paper. It will give you some very important information about using stepper motors. That paper is outdated, particularly the part about selecting a power supply, but the general information is good background information.)

3. Connect the break-out-board to the Gecko stepper drivers
- Terminal 7 is usually left disconnected
- Terminals 8 is connected to the appropriate Direction signal on the break-out-board
- Terminals 9 is connected to the appropriate Step signal on the break-out-board
- Terminals 10 is connected to +5VDC on the break-out-board

(I haven't used that particular break-out-board, so you'll have to research the documentation. Send me an email if you run into difficulty and I'll try to help.)

4. Install Mach 3 software on your computer

5. Test until you're confident that everything is working.

You'll have to add the appropriate safety devices; i.e. switches, fuses, contactors, and disconnects, but that is part of building your own controller. It's not difficult, but take your time and understand what each part does before adding it to the circuit.

You'll note that all the motors turn the same direction if you've followed my instructions. To reverse the direction of one of the X-axis motors, exchange the Black and the Green wire on the appropriate Gecko. That will cause the stepper motor to turn the other direction.

One last note. The G201 is an excellent stepper driver, but it is obsolete. Gecko now recommends the G201x or the G203v stepper drivers. They are more robust and they run significantly cooler. I've never used the G201. My first project was started after Gecko released the G202 stepper driver. Those G202 drivers are still running perfectly after at least four years to rough and tumble testing. Also, I much prefer the PMDX-122 break-out-board to any others that I've seen. The PMDX-122 is relatively inexpensive (about $85) and it works very well.

-----

That is a very simplistic outline of what you'll have to do.

Shopbot's 4G upgrade will let you continue to use Shopbot software and you won't have to spend a lot of time learning electronics. For most people, the price of the 4G is money well spent (unless you're like me, a process computer designer who would rather tinker with electronics than cut wood).

[richards]

Sometimes change is beneficial.

I don't have all the facts about the original PR and PRT machines, particularly facts about the stepper drivers used in those machines; however, before Gecko, it was common to use stepper drivers that used full steps (200 steps per shaft rotation) or half-steps (400 steps per shaft rotation). Gecko's stepper drivers have 2,000 steps per shaft revolution.

However, from the unit values Rick posted, assuming that he has motors with 3.6:1 gearboxes, it appears that he has a machine that has stepper drivers that produce 800 steps per motor revolution. It also appears that if the motors are geared 3.6:1, that he has 25-tooth pinions on the on the X and Y axes,and a 20-tooth pinion on the Z-axis.

Changing to Gecko stepper drivers would give 2.5X better resolution (smaller distance moved per step).

The unit values would become 1833.4649 for the X and Y axes and 2291.8312 for the Z-axis.

[RickWyatt]

Thanks to everyone again! I am very luck to have so many supportive people here to help.

There were some difficulties with the site last evening and I replied to Mike via email. I will post my reply here so that others could follow the conversation for help as well:

Mike,

Wow! Thank you!

This community is amazing. I hope to be able to contribute back as soon as possible. I think documenting this process and putting it all in one place will be a great start.

Thanks too for the g-code warning. However, I would prefer g-code. I was a part of the exhibit and display industry for 14 years drawing,programming and running Komo and AXYZ machines. So, I am actually lost looking at the Shopbot code. I recently stepped out on my own and have my Shopbot and a 30watt laser from Universal. I am capturing a niche' area of the exhibit and display industry that seemed to be missing.

As far as the toroidal transformer goes, I'll have to figure out the VAC somehow. It does have a bridge rectifier on it that is marked 600v.

On the G201's: they came with a resistor in positions 11 &12 as you said. One of the drives came with 2 resistors in those positions. Not sure why? But I can check the resistance on those to be sure.

I figured those 201's were older. I will probably still use them just to keep costs down.

Although I don't have a lot experience with the electronics, I think by learning the how's and why's will help me to produce the best parts possible on this machine. Not to mention, less down time when something goes wrong.

Thanks again, MIke, I sincerely do appreciate the detailed help. I hope I could return the gesture in some way. Please feel free to let me know if you need anything.

Rick Wyatt

[RickWyatt]

use 18 tooth pinions...a cheap way to go and will help but you will loose speed.

you start upgrading your speeds then the mechanical problems will rear their head...then you want to upgrade that...then another upgrade then another....that is how the mechmate was born.

Gene,

You mention, yet, something else I need to learn about. I will look at my documentation I received with the machine when I get back to the shop on Monday. I will count the teeth on my rack and pinion to post here along with my gear box ratio.

Rick

[jim_mcmillan]

These two Yahoo groups should help as well.
http://finance.groups.yahoo.com/group/geckodrive/?yguid=234504003
http://groups.yahoo.com/group/mach1mach2cnc/?yguid=234504003

By the way, I'm the guy who originally owned those Geckos, and I bought the transformer and rectifier new from an electronic supplier. I traded it off to a buddy of mine in MN, who did some trading with another guy in MN, where I'm guessing you got it from. I think I bought two of the Geckos brand new, and two I got used off of e-bay several years ago. I never finished the system so never ran any of them, but there's no reason to believe they won't work as new. I don't remember the numbers, but the transformer and rectifier were sized specifically for running at least three Geckos up to full power, so I think you'll be alright there unless I screwed up the math. It's been a few years, but I may be able to dig up something on the transformer if there are no ratings marked on it. Let me know. It was set up for standard US 110VAC in, and I think the output was 48VAC as wired. With a hefty filter cap you should see something in the high 60s DC, no load. The Geckos are rated at 70VDC max input. You'll need to change the current set resistors to match your motors, so I wouldn't worry about what's on there now. I'm not too sure about how to set up your specific motors with the Geckos, but others here are. Also, the Gecko site and the Yahoo forum are great sources. Mach is a nice program and you shouldn't have much trouble if you're familiar with g-code and machine controllers in general. As for resale value of a "bastard bot", well, that's another story. I suppose you could always do some more horse-trading and put it back to stock if the need arises!
Anyhow, it'll be nice to see this stuff finally put to work! Keep us posted.
Cheers,
Jim McMillan

[richards]

There are some simple math formulas which make size a transformer easy.

MAXIMUM voltage for a stepper motor:

32 X SQRT (Inductance) = MAXIMUM voltage

Example:

32 X SQRT ( 7.7 mH ) = 88.8 Volts

However, a Gecko's maximum voltage is 80VDC, so the maximum voltage for that motor will be limited to 80VDC. (My tests have shown that a stepper motor run at its maximum voltage will get really hot, about 80-degrees C, but it will also run fast, 2,000 RPM or higher, depending on the physical size of the motor. CNC machines don't like hot and they don't need fast, so a power supply rate at 75% of the motor's maximum allowable voltage works just fine.)


The formula for sizing a transformer is:

1 / SQRT(2) X DC voltage = AC required

or

AC X SQRT(2) = DC voltage

Example:

You want an 80 VDC power supply, so:

1 / SQRT(2) X 80V =

0.707106781 X 80 = 56 VAC

You have a 50VAC transformer. What is the expected DC voltage?

50VAC X SQRT(2) = 50VAC X 1.414213562 = 70.71 VDC

(Those figures assume no that there is no diode drop loss, which is about 2V per bridge rectifier and they also assume that the input voltage to a transformer rated at 115VAC is exactly 115VAC. In reality, small differences will occur, but stepper motors don't really care about small differences.)

Next, how much current must the transformer provide? Add up the current requirements of all the motors and multiply that figure by 66%. (Remember, a CNC machine will not run all the motors at full power all the time. Mariss, at Gecko, recommends the 66% figure.)

1.5A X 4 motors = 6A and 6A X 66% = 3.96A

Multiply the transformer's AC voltage by the current required:

50VAC X 3.96A = 198VA

Your transformer needs to be at least 200VA, although I would use a 250VA or 300VA model. They cost about the same and they would allow you to tweak the motors' output current a little.

How about the output capacitor? Use this formula:

80,000 X Amps / DC Voltage = Capacitor in uF.

Example:

80,000 X 4A / 70VDC = 4,571 uF

In this case, more is better, so use at least a 4,500 uF capacitor and a 6,000 uF or higher does no harm.

Capacitors are also rated for the voltage that they can handle (sometimes called breakdown voltage or working voltage). It's a good rule to use a capacitor that is rated to handle voltages at least 50% higher than the DC voltage of your power supply. If the working voltage is too low, the capacitor will start to heat up and the dielectric material will dry out which will ruin the capacitor.

[jim_mcmillan]

Mike,
You got me on the Gecko's max voltage. I double checked and it is 80, not 70 as I thought. I also may have mis-stated about the power - I said that transformer was intended to handle full power of 3 Geckos, but that would be take something like a KW and I don't think that transformer is that big. I think what I had in mind at the time was to run my Taig mill with it's 3 amp steppers. That points towards more like 500VA.
It might be this one:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1358-ND
It's probably marked, but if not it's pretty easy to estimate the power rating simply by the size and weight. Find something close in a catalog and you'll be in the ballpark.
Are those numbers (7.7mH and 1.5A) correct for the old Shopbot motors, or just given as an example? I've heard they use some pretty high-inductance motors. Just out of curiosity, what voltage do the Shopbot controllers run at?
Cheers,
Jim McMillan

[richards]

Jim,

Those motors, if they have only four leads, have 30.8mH inductance. If they have six leads, they can be wired half-coil and they will only have 25% as much inductance (7.7mH).

In either case, the computed voltage is higher than a Gecko can handle, so you would have to use a power supply of 80VDC or less.

They are rated at 1A when wired bipolar series and at 1.5A when wired half-coil or unipolar; however, because of the fact that they will be run at a reduced voltage, they could be allowed to draw more than the rated current. Heat is watts and Watts = Amps X Voltage. The computed maximum voltage shows that the motors is rated at 177 watts, but 80V X 1A only generates 80W, so the brave have room for experimentation.

A transformer producing 56VAC will generate 80VDC and 4 X 1A = 4A, so 4A X 56VAC = 224VA. That could safely be reduced to 66% of that value because not all of the motors wold be pulling maximum current at the same time; however, there is not much difference in the price of a 250VA, a 300VA and a 400VA transformer. As a general rule, I use a 500VA transformer unless the computations show that I need to go bigger than that.

If the transformer gets too hot to touch, I would recommend getting one that can handle more current. Most transformers have a class B insulation rating, meaning that they can handle an 80-degree C temperature rise with a maximum temperature of about 100-degrees C. That's too hot for me. In any case, toroidal transformers have never gotten even warm to the touch on my test bench, even when the motors were too hot to touch.

I used the figures of 7.7 mH and 1.5 mH as examples. They are the values of the PK296A1A-SG3.6 motor and of the PK296A2A-SG3.6 motor when those motors are wired half-coil. Half-coil gives much higher top end speed. Just yesterday, I was testing some motors. I had a PK299-F4.5 spinning at over 2,000 RPM on a 47VDC power supply. (I limited my PK296B2A-SG3.6 motors to 1,500 RPM. (the B means that the motor's shaft extends out the back of the motor so that an encoder can be attached). The gear boxes on those motors have a limit of 500 RPM, so I didn't want to destroy perfectly good gearboxes in my quest for speed. Those B2A motors were also run from that 47VDC power supply with very moderate temperatures about 40-degrees C. That's because Oriental Motor underrates those motors from 4.5A to 3A when they're attached to a gear box. The formula 32 X SQRT(1.5 mH)= 39VDC, so you can see that, according to the formula, I should have used a power supply of 39VDC or less; however, 39V X 4.5A = about 175W and 175W / 3A = 58V. So, in theory, I could have used a 58VDC power supply before generating maximum heat.)

Many people really get uptight when they're designing controllers for stepper motors. I run the numbers to see what would work best and then I do some testing to see how things work in the real world. If things get too hot, I reduce either the voltage or the current. If the motors can run faster than I need, I reduce the voltage. If I've reduced the voltage, I increase the current a little to get additional torque. It's sometimes a matter of trade-offs. What are you willing to give up to get what you need? Sometimes you need more speed. Speed depends on voltage. The higher the voltage, the greater the possibility of speed. Voltage X Amps = Heat, so, if you raise the voltage, you'll probably have to reduce the Amps that the motors are allowed to pull.

The experimentation is easy when you use Gecko stepper drivers. You can attach any power supply to them that produces at least 15VDC (to 24V, depending on which G20x model you're using), but not more than 80VDC. The Gecko's have either dip switches or terminals where you select the value of the current limiting resistor. If you have a Variac on your test bench, you can dial the voltage of the toroidal transformer up and down until you find the perfect solution, then you just order a transformer that matches your specifications.

[jim_mcmillan]

Hi Mike,
I'm afraid we sort of hijacked Rick's thread, and may be guilty of "information overload"... Sorry Rick.
Anyhow, since we've gone this far, why stop now?
So I looked for info on the A6497-9412KTG motors that Rick said he has on his bot. The Oriental Motor site didn't have anything about it online, but a Google search turned up a reference to it on CNC Zone. It was described as "2 Phase, 1 Amp, 4.39 ohm". That is second-hand info, and it conflicts with Mikes info so I'm not sure what to believe. At any rate, it doesn't really matter that much. the Geckos won't complain either way. Just make sure you install the right current-set resistors per the Gecko manual else you risk overheating the motors.
The bottom line as far as I can figure is that that toroid is probably way bigger than needed, which is fine, and the voltage should fall in the mid to high 60s after rectification and filtering, which should also be fine with a comfortable margin. Just put a 5000 to 10000 uF electrolytic cap with a voltage rating of at least 100V across the rectifier output, and the power supply is ready to rock.
Jim

PS. Mike, that first line in your last posing is confusing me a bit. Wouldn't half coil give you half the inductance rather than 1/4 as you stated, or did I misunderstand your meaning?

[richards]

Jim,

On the Oriental Motor site, the PK296A1A-SG3.6 motor is rated 4.4 ohms, 1A, 30.8 mH inductance when wired bipolar series. The same motor is rated 2.2 ohms, 1.5A and 7.7 mH inductance unipolar.

Unipolar values are used for half-coil connections.

The inductance rating is confusing. Just as you said, it would seem that half-coil would give half the inductance of full coil, but that's not the way it works. Sometimes you just have to trust the manufacture.

The reason that you can play with the current limiting resistors and exceed the maximum current rating on those motors is because of the limitation on voltage when those motors are driven with a Gecko G20x stepper driver. Those stepper drivers are limited to 80VDC.

The computed ideal voltage for that motor, when run bipolar series is 177 volts. The Gecko stepper driver can't handle 177 volts. The heat produced at 177V X 1A would be 177 Watts and 177 Watts / 80 V = 2.2 Amps. So, the brave hearted could experiment with current limiting resistors. I'm guessing, from my experimentation with other motors, that you could safely run that motor at least at 1.5A and probably at 2A before it got uncomfortably hot.

It's my understanding that the A6497-9412KTG motors were shipped with only four wires exiting the motor; a black wire, a green wire, a red wire and a blue wire. That indicates that the motor can only be connected bipolar series. That's too bad, because the motor would have much better speed if it were wired half-coil.

Be certain that you have jumpered the stepper drivers to enable auto-current-reduction if you increase the current beyond 1A. Auto current reduction automatically reduces the current of an idle motor to 30% or 50% of normal (depending on the stepper driver). It does that to keep the motors at a safe temperature when they are idle. Much of the problems that have occurred from overheating stepper drivers was caused by turning off the auto current reduction and by not having heat sinks mounted to the stepper drivers. The G201, in particular, gets hotter than the newer G201x or G203v. The G201 uses different internal circuitry that drops more voltage across the transistors and the transistors have higher junction resistance than the newer models, which means that more heat is created. Properly setting the auto-current-reduction jumper and using a heat sink solves that problem.

I agree with you, Jim, in that you work with what you have. There in nothing wrong with using those parts. They will work. However, if someone were to buy new parts, they should look carefully at the Gecko G201x or the G203v. They should look at the Oriental Motor PK296A2A-SG3.6 motors instead of the PK296A1A-SG3.6. They should use a power supply in the 35VDC to 48VDC range if they use the A2A motors.

[jim_mcmillan]

Could be they're talking about a parallel hook-up on an 8-wire motor vs. series hook-up. That would explain the 1:4 inductance ratio.
I haven't tried "over amping" motors as you suggested, and probably wouldn't recommend it except for "power users" such as yourself who like to experiment. That said, stepper motors are pretty bullet proof.
Anyhoo, the motor that Rick has is A6497-9412KTG. Do you know where to find the specs on that one?

[Brady Watson]

I feel a lot of "mechanical vibration" when my machine moves in x and y axis. If I Put my hand on the Y carriage, I can fell it "Mechanically shake" during all types of movements.

Don't read if you have a PRS...This applies to PRTs only

Regardless of what electronics, motors and software you use to drive your PRT iron, there are still a few maintenance issues that you'll want to tackle ASAP.

Pinions and racks should have grease on them. Don't slather the grease, just keep them wet. When your cut quality degrades, it is telling you that you need to do maintenance. The following 3 areas may need attention:

1) Pinions - PRTs with A6497-9412KTG (3.6:1 motors) should have 25T pinions to run correctly. 16s, 18s & 20s wear very quickly & only have one or two teeth at most engaged in the rack, which makes them wear faster & exhibit cogging tendencies. When you order pinions (cheap) order 2 sets. Compare your old ones to new ones. Also, the proper tension on a PRT motor turnbuckle is 3.5 turns after the spring just gets tension. Any more & you'll prematurely wear out pinions - too lose & you'll skip teeth.

2) Matted down/forged & dirty rails where the v-roller bearings have worn a groove into the angle rails. Dress the rails with a file and sandpaper or scotch pad. This makes an unbelievable difference if you have not been maintaining them. Closely look at the rails - carefully run your hand over them - any little sharp edges or bumps you feel act like boulders when v-rollers hit them. Clean 'em up & maintain them with a brown 3M scotch pad.

3) V-roller bearing adjustments on Z axis/t-rail as well as lower bearings (side to side) on Y car. You should get in the habit of grabbing each axis with power on & no movement - and shake the heck out of it. Look, listen and adjust.

If you are going to add more power or speed to this down the line, there are a few things you will NEED to beef up. If running 3/8" Boston gear rack there isn't enough meat to support higher loads & speeds. You'll want to bump up to a 1/2" Browning rack & suitable 1/2" wide pinions to match. You'll want to machine yourself some 1/4 or 3/8" X & Y motor mounting plates out of AL or steel IF you have the single 1.5" angle iron motor mount with little 3/4" angle spring perch on them. They are way too flimsy for speeds over 4 IPS. You'll want to gusset the table like a late PRT or PRS tool. And last, but certainly not least, you should toss the gold utility strut on the gantry & replace with 1.5 X 2.5" box steel. Weld it to the 3X3s and also tack the Y rails to the 3X3s on each end of the X car. You'll never rack the gantry again...

-B

[richards]

I follow closely several different forums, each one hosted by the manufacturer of a CNC machine. When I'm posting to those different forums, I like to think that cross-talk between forums might cause some hurt feelings. Each design has good points and each might have some weaknesses, but Shopbot is a great company with a very good machine. It's not perfect just as none of the other machines that I follow are perfect, but I try not to compare features or to list limitations when visiting the various forums.

Sometimes sending a private e-mail would be the better way to help.

[richards]

Gene,

I think that you would agree that that post was in direct response to a question from someone who wanted to mix and match electronics from his Shopbot onto another type of machine. I think that you would also agree that I cautioned him about using older Shopbot electronics with known issues when other options were available.

I've done the same thing here, on the Shopbot site. When 'botters have asked about the feasibility of using Mach 3 and hardware designed for Mach 3 on their Shopbots, I have tried to point out that they would lose compatibility with Shopbot software, which is one of the main reasons that people buy a Shopbot.

When people ask a direct question, i.e., when they mention the competition, I give a direct answer. I try to be as fair-handed as possible while giving factual information. Sometimes my responses might be taken as being 'unkind', but they're not meant to be unkind.

Have you noticed that each of the 'faults' that I listed in that post have been corrected in the latest Shopbot controllers? Like any good company, Shopbot pays attention to complaints and concerns and eliminates the problems whenever possible.

The Shopbot PRS models are FAR superior to older models. The PRT-Alpha that I owned was FAR superior to the models that came before it. Each generation is better. Each generation of software is better. Each generation of electronics is better. Each machine, Shopbot or competitor, was designed to fill a niche. Shopbot has continued to improve their mechanical designs. Some of the designs of other manufacturers have remained static, without any substantial changes.

Personally, if I were building my own machine, I would model it after the PRS. (I would drop the side rails to table-top height and I would use linear rails and trucks rather than V-rollers, but other than that, I really like the basic design of the machine.) Of course, given my age, and my general health, I will never build my own machine.